Humans’ ability to attribute mental states to agents has been hypothesized to underpin our unique social behaviors. However, questions remain about the extent to which our representational Theory of Mind (ToM) is shared with non-human primates (NHPs). Here, we present a set of computational models each built to formalize a different representational theory of a foundational ToM component—understanding what others can see—and compare each model’s performance to that of NHPs across a range of previously published perspective-taking experiments. Our results show that multiple competing theories can account for NHPs’ perspective-taking abilities, including both human-like ToM and less complex mentalistic theories, but not simpler, non-mentalistic theories. This work supports the idea that NHPs may reason about others’ mental states when assessing their visual perspectives, and provides promising avenues for future work using computational modeling to determine if and how NHPs represent more complex mental states (e.g., ignorance, belief).

Theory of Mind (ToM) is central to human social cognition, yet the roots of this capacity remain poorly understood. Both infants and nonhuman primates perform inconsistently on false belief tasks, limiting our understanding of the representations that characterize their ToM. Here, we seek to better understand this often-contradictory literature by dissecting these failures. Specifically, we focus on primates' characteristic null performance on false belief tasks. Across three studies, we find that—despite succeeding on a closely-matched control—rhesus monkeys fail to predict how agents with false beliefs will behave even when the agents perform highly unexpected, unlikely actions. We interpret this pattern of performance as evidence that monkeys have no representation of another agent's past awareness once the scene changes outside of that agent's view. This work moves beyond the success/failure dichotomy typically used to assess ToM, and instead gives a more precise characterization of primates' signature limits in ToM.